Rocket apparatus employing electrolysis



July 14, 1970 NEWMAN ET AL 3,520,137

ROCKET APPARATUS EMPLOYING ELECTR"LYSIS Original Filed Feb. 27. 1967 4Sheeis-Sheet 1 Gaseous Propellanf I Control I VO'VB V Pressure SwitchDoniel D. Newman, 98 Harold A. Rosen, INVENTORS. l, BY

Liquid 90 Pro II t 92 33, 1" ALLEN A. DICKE, Jr.,

Valve AGENT July 14, 1970 D, D EW ET AL 3,520,137

ROCKET APPARATUS EMPLOYING ELECTR LYSIS Original Filed Feb. 27, 1967' 4Sheets-Sheet 2 57 Flash buck orresfor Fig. 6.

Daniel D. Newman,

Harold A. Rosen,

INVENTORS.

ALLEN A. DICKE, Jr.,

AGENT.

v y 4, 1970 D. D. NEWMAN ET AL ROCKET APPARATUS EMPLOYING ELECTRCLYSISOriginal Filed Feb. 27, 196+ 4 Sheets-Sheet 15 Control Chopper swnchCircuit I Voltage Trigger Rgtfcrueiq circuit V lropell|ant ontro 2Pressure 52 23 Switch r i I Control Dc DC swnch Converter VoltageReference 7 Circuit c'rcun Daniel D. Newman, Harold A. Rosen,

INVENTORS.

ALLEN A. DICKE, Jr,

AGENT.

July 14, 1970 D, D, NEWMAN 1ET AL 3,520,137

ROCKET APPARATUS EMPLOYING ELECTRCLYSIS Original Filed Feb. 27. 1967 4Sheets sheet 4 Fig. 7.

76 Water absorbent wick Daniel D. Newman, Harold A. Rosen,

INVENTORS.

ALLEN A. DICKE. Jr.,

AGENT.

United States Patent US. Cl. 60221 Claims ABSTRACT OF THE DISCLOSURE Therocket propulsion apparatus employs propellant which is stored as aliquid and which is electrolyzed to generate gaseous propellant asneeded. The gas is either burned in an engine or employed in the coldgas technique. The generated gas can also provide pressure to feedliquid propellant to an engine.

CROSS REFERENCE This is a division of application Ser. No. 618,651 filedFeb. 27, 1967, which in turn is a continuation-in-part of applicationSer. No. 542,709 filed Apr. 8, 1966, now abandoned, which was, in turn,a continuation of application Ser. No. 374,012 filed June 10, 1964, nowab'andoned.

BACKGROUND This invention relates primarily to a thrust producing systemand in a preferred embodiment to a spacecraft reaction control systemfor imparting the small impulses needed over long periods of time formaking fine adjustments in its orbit.

Many spacecraft require an internal propulsion system which is capableof frequent firing or pulsing for short time durations over a longmission lifetime of weeks, months, or even years. Synchronously orbitingcommunication satellites, for example, require a propulsion system tocorrect for the variations in its orbit due to the apparent east-westdrift perturbation resulting from the triaxiality formed by thenon-spherical distortion of the earth and also due to the north-southinclination changes resulting from solar and lunar gravitationaleffects.

Previously available propulsion systems for spacecraft impart therequired impulses by the decomposition of liquid monopropellant such ashydrogen peroxide or hydrazine in a combustion chamber and by expellingthe resulting gaseous products of decomposition through a nozzle.Stability of monopropellants is limited and slow decomposition limitsthe useful mission lifetime. The specific impulse (ratio of developedthrust to propellant consumption rate) is low; therefore, for a giventhrust, consumption of propellant is high. Propulsion systems are beingdeveloped for orbital vehicles which employ separately stored liquidfuel and oxidizer. The two fluids are brought together in a combustionchamber and react on contact. In the small engine sizes required fororbital vehicles, the proper injection and mixing of liquid propellantsrequires extreme precision in the manufacture of injectors. The smallholes are subject to clogging by particles, gums, or sludges. Specificimpulses of these systems are higher than with a monopropellant. Longterm storage of these propellants during an extended mission isquestionable as they are corrosive and tend to sludge. The use ofgaseous propellants eliminates many of the problems associated withliquid propellants; however, the storage of pressurized gas inquantities needed to perform long term missions results in excessivetank weight, and this type of system is subject to the disadvantages ofgas leakage, and low performance toward the end of the mission when thegas pressure is reduced.

SUMMARY In order to aid in the understanding of this invention, it canbe stated in essentially summary form that it is directed to a rocketapparatus which employs electrolysis. A vessel stores electrolyzableliquid. Electrodes are in contact with the liquid so that upon theapplication of current therebetween, the liquid is electrolyzed toproduce a gas. This gas pressurizes the vessel. The pressurized gas isused to expel the liquid, or to expel the gas in cold gas expulsion orfor burning of the gas as it is expelled (if the gas is combustible).The apparatus may be arranged to operate in several of these modes, ifdesired.

It is a primary objective of the present invention to provide a thrustproducing system which is capable of frequent firing for short timedurations over a long mission lifetime. Another object of this inventionis to provide a propulsion system which stores a propellant in an inert,stable fluid state for long time periods. Yet another object is toprovide a propulsion system which generates a pressurant from a storedinert stable fluid and which utilizes the pressurant for propellantexpulsion.

Still another object is to provide a propulsion system which generates ahigh energy propellant as needed for intermittent propulsion over a longtime period or mission lifetime. Still another object is to provide apropulsion system of the above type which can operate under zero gravityor near zero gravity conditions for extended periods of time. Yetanother object is to provide a propulsion system characterized by thestructural simplicity of monopropellant systems and the high performanceof bi-propellant systems.

Yet another object is to provide a propulsion system which collects andstores solar energy as electrical and chemical energy for laterutilization of the chemical energy at high rates of expenditure. Anotherobject is to provide a highly reliable bi-propellant system in which themixture ratio of the propellant cannot shift and the response time isfast and thrust can be accurately and easily controlled. Still anotherobject is to provide a propulsion system which requires decreasinglyamounts of power to operate as mission time increases.

These and other objects are accomplished according to a preferredembodiment of the present invention in which the thrust producing systemis incorporated in a satellite by subjecting a quantity of water andpotassium hydroxide stored within an enclosed chamber to electrolysis,to evolve or generate the high energy bi-propellant comprising hydrogenand oxygen gases which are stored under pressure until needed. Then,upon command, the stored bi-propellant gases are fed to an engine andignited to provide thrust for accurately controlled short time durationswhile at the same time flashback of the ignited gas into the propellantstorage portion of the system is prevented. Once the stored gas fallsbelow a certain level and/or once it is again necessary to producethrust, the electrolysis action is again initiated and continued untilthe necessary gas pressure is obtained.

In another preferred embodiment of the invention, the generated hydrogenand oxygen gases are employed as a propellant by means of the cold gastechnique (they are expelled from a nozzle without burning). In stillanother embodiment of the invention, the electrolyzable material is notwater but is a propellant in the liquid state and is used as such whenit is desired to produce higher amounts of thrust (the liquid is fed toits engine under pressure of the generated gas) but which is elec- 3trolyzed to generate gases which are used to produce relatively smalleramounts of thrust by either burning the gases or using them in the coldgas technique.

These and other objects and advantages of the present invention will bemore fully understood by reference to the following description, theclaims and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram whichillustrates the basic principles of the present invention.

FIG. 2 is a perspective view of a synchronously orbiting spinningsatellite showing an engine arrangement.

FIG. 3 is a partly cross-sectional, partly elevational view of thepropellant generating tank of FIG. 1.

FIG. 4 is a graphical illustration of a predictable propulsion pulsewaveform.

FIG. 5 is a schematic electrical block diagram of a portion of theelectrical control system pertaining to one of the propulsion engines ofFIG. 1.

FIG. 6 is a side elevational view of a propulsion engine illustratedpartly in cross section to show the relationship of an ignition sparkplug and combustion chamber with a porous flashback arresting plug.

FIG. 7 is a side elevational view partially in cross section of anembodiment of the invention in which an electrolyzer or gas generatorwithin the chamber includes a water absorbent wick which maintains waterbetween a pair of concentric electrolyzing electrodes by means ofcapillary action.

FIG. 8 is an enlarged side cross-sectional view of the electrolysis cellof FIG. 7.

DESCRIPTION FIG. 1 illustrates a hybrid system of the present invention.This system comprises a pair of spherical tanks 18 and 19 definingenclosed spherical chambers 20 and 21 for storing propellant in theliquid state. The chambers 20 and 21 in addition to being storagechambers are also electrolytic cells since the liquid propellant issubjected to electrolysis to generate gases in the chambers 20 and 21.The hybrid system shown in FIG. 1 includes a pair of engines 28 and 29,of the type which use gaseous propellant, connected to the gas ullagespace in the chambers 20 and 21 and a pair of engines 90 and 92, of thetype which use liquid propellant, connected to the portion of the tanks18 and 19 containing the liquid propellant.

In the hybrid system the preferred material for use in the chambers 20and 21 includes such materials as hydrogen peroxide and hydrazine. Thehybrid system allows the integration of a conventional hydrogen peroxidesystem and the electrolysis system of the present invention into asingle system which can both burn the hydrogen peroxide directly forhigh thrust and electrolyze it and burn the resulting gases. Theeventual decomposition of hydrogen peroxide, to water, after years inspace does not disable the system as the water is then electrolyzablealong with the residual peroxide. This system also does not rely onstored pressured nitrogen gas to feed the hydrogen peroxide to itsengines as it makes its own pressurized gas by electrolysis. This hybridsystem eliminates the disabling of a system due to leakage of gas andalso eliminates the low performance of prior systems toward the end ofthe mission when the nitrogen gas has expanded to low pressures. Thehybrid system, or dual mode operation, is also available usinghydrazine. The diiference between the hydrogen peroxide gas and thehydrazine gas is that the gas generated by electrolysis using hydrazinedoes not burn so that its use is limited to use in the cold gastechnique and it is limited in that hydrazine decomposes into ammoniainstead of water.

Once a predetermined gas pressure is obtained, a pressure switch 23 isactuated which signals a control circuit 24 to stop the electrolyzingaction, for example, by disconnecting the power supply from theelectrolyzing electrodes. Separate command signals from the controlcircuit 24 are in turn used to selectively open a pair of normallyclosed electromagnetic or solenoid propellant control valves 26 and 27to allow the generated gas to flow to the reaction engines 28 and 29respectively. When using a material in the chambers 20 and 21, thegenerated gas of which is combustible, at the same time that thesolenoid valves 26 and 27 are opened, a pair of spark plugs 30 and 31 ineach of the engines 28 and 29, respectively, are energized to ignite thegases in the engine combustion chamber thereby developing a reactionforce through each engine nozzle. If the apparatus were designedspecifically for use in the cold gas technique (i.e. with a gas whichdoes not burn), the spark plugs 30 and 31 and the corresponding portionof the control circuit 24 would be eliminated from the design. However,the cold gas technique could be used with engines designed specificallyfor use with gases which do burn. The pair of engines and 92 aresupplied with liquid propellant from the chambers 20 and 21 via a feedline 94 which taps into an equalizing line 43. The liquid propellant iscontrollably fed to the engines 90 and 92 by means of a pair of solenoidactuated propellant control valves 96 and 98. The valves 96 and 98 areactuated by signals received from the control circuit 24.

When the gas engines (or the liquid engines or both) of FIG. 1 areutilized for the station keeping of a synchronously orbiting satellite(FIG. 2), one engine 29 would be directed along the satellite spin axispreferably radially displaced therefrom while the other engine 28 wouldbe directed radially outward of the spin axis preferably in the plane ofthe center of gravity of the satellite. Thus, the axially directedengine 29 would be energized in a somewhat steady manner to overcome theelfects of solar and lunar gravitational attraction on the satellite.The radially directed engine 29 would in turn be pulsed periodicallyduring a predetermined segment or sector of satellite spin to overcomeeast-west drift. A spinning satellite is usually placed into orbit in aspinning condition by action of the final stage of the launch vehicle.However, the rocket engines of the present invention can be used theestablish, maintain and control the spin of a spinning satellite.

Referring back to the spherical electrolysis tanks of FIG. 1 in moredetail, each tank is symmetrically arranged about a central spin axis(see the arrow in FIG. 1) so that the material contained within thechambers is centrifugally forced radially outward of the spin axis. Eachchamber is made of carbon steel or other equivalent high tensilestrength electrically conductive material and can be nickel plated toeliminate the problems of oxidation. Each chamber includes a concentric,cupped, electrolyzing anode electrode 3 and 4 respectively, each ofwhich is made of a nickel wire mesh or screen and are spaced from thechamber wall at the radially outermost portion thereof by anelectrically insulating bushing or mounting 36 (FIG. 3). An electricalcurrent supply lead 37 extends through the wall of the spherical chamber21 to supply current to the anode electrode 33 at a potential positiverelative to a ground or reference potential. The spherical tank is inturn connected to a ground terminal, thereby providing a cathodicelectrode surface relative to the anode screen electrode 33. As currentis supplied to anode electrode 33 bubbles of gas are generated at thesurface of the anode and the cathode. These lightweight bubbles of gasescape to a ullage space which is diametrically opposite the anode 33and slowly build up a reservoir of pressurized gas within the chamber.

Liquid material is initially added to the spherical chamber through afill valve 41 which can be of the type having a spring pressure andinternal air pressure seated valve stem. One commercially available typeof valve which can be used is the Deutsch Companys fill and drain quickdisconnect Model DQC, illustrated in Catalog No.

DH-62004, printed August 1961. The tank is not completely filled, asspace must be left for generated gas.

Referring back to FIG. 1, weight balance about the spin axis is effectedby the equalizing line 43 connected to communicate between the radiallyoutermost ends of the two spherical chambers 20 and 21 so that liquidtransfers from one tank to the other by centrifugal force when theybecome unbalanced. Some advantages of this equalization is the tendencyto correct for any spin imbalance in the satellite while insuring thatone chamber will not run dry before the other in situations where one ofthe electrolyzers consumes liquid faster than the other.

Once enough gas has been generated such that the pressure of thegenerated gas in the ullage space and in the gas manifold 46, which isconnected through each of the tanks 18 and 19 at an inner-upper wallportion, reaches a predetermined pressure sufiicient to close thepressure switch 23, the control circuit 24 in response to the closing ofswitch 23 stops the electrolyzing action. Thereafter, the generated gaswill remain in the ullage space under pressure until such time as it isneeded.

The above described electrolysis operation can be readily accomplishedby an electrical control circuit, of the type illustrated in FIG. 5.Subsequent to the start of the mission, a control signal is transmittedto a command circuit (not shown) to actuate a control switch 47, therebyinitiating the fiow of electrolyzing current to the storage andelectrolyzing tank 18. This command circuit can be of any conventionalwell-known type such as that being used in the SYNCOM Satellitemanufactured by Hughes Aircraft Company. Actuation of the control switch47 conducts energy from a power supply terminal bus 48 which includes aDC storage battery 49 which is in turn connected in circuit with a solarcell panel 51. This solar cell panel can be any conventional type suchas the type used in the above referenced Hughes SYNCOM Satellite andconsists of a plurality of silicon N on P fiat rectangular cells eachcapable of generating electric energy of a half volt and 50 milliamps.By connecting these cells in series columns to raise the voltage and thecolumns in parallel to increase the current, sufiicient power isgenerated to operate the circuit.

The control switch 47 is essentially a conventional electromechanical orelectronic switch used to apply the DC power to a DC-DC converter 52which, in turn, provides a constant current variable low voltage (around2 volts) output for electrolysis of a liquid in the tank 18. This DC-DCconverter can be of a conventional type such as described on p. 439 ofTransistor Circuit Design edited by the engineering staff of TexasInstruments, Inc. and published by McGraw-Hill Book Company. For circuitoperating stability a voltage reference circuit 53 is connected toreceive the power signal from the output of the control switch 47 andprovide a stable reference voltage for close frequency control of atrigger circuit 56. The voltage reference circuit 53 can be aconventional type such as described in Fig. 9-8 on p. 153 of the abovereferenced Transistor Circuit Design book. The trigger circuit 56receives the reference voltage and provides isolation between thevoltage reference circuit and the DC- DC converter 52, thereby assuringstable and reliable operation of the converter under all loadconditions. One type of trigger circuit which could be used would be aSchmitt trigger illustrated on p. 169, Fig. 11.10 of the GeneralElectric Transistor Manual, edited by General Electric, 6th ed. Theoutput from the trigger circuit 56 is connected to externally triggerthe DC-DC converter so that a rectified constant current (about 2 amps)is supplied to the anode electrode 33.

A pressure-sensitive switch 23 is connected to sense the gas pressureand effect electrolysis only when the pressure drops below apredetermined level. Pressure switch 2 3 can be any conventionaldiaphragm type 'which actuates a microswitch or limit switch when thepressure exerted on one side of the diaphragm exceeds a predeterminethreshold level. When the pressure switch is actuated, the controlswitch 47 is open circuited to de-energize the DC-DC converter and stopelectrolysis. When the gas pressure drops below a predeterminedthreshold level, however, the pressure switch 23 is deactuated to againswitch on the control switch 47 to apply current to the DC-DC converter52 to again initiate electrolysis. This cycle is continued throughoutthe life of the mission.

When propulsion forces are desired, either one or both of thefast-acting solenoid valves 26 and 27 of FIG. 1 are selectivelyenergized thereby releasing the pressurized gases for flow into anengine such as into the combustion chamber of the engine 28 or 29. Thesevalves can be any commercially available solenoid type valve which has afast opening time on the order of two to eight milliseconds.

In another preferred embodiment of the invention the electrolyzableliquid which is used is Water. All of the apparatus shown in FIGS. l-8is applicable for use in a system using water for fuel with theexception of the engines and 92 and associated equipment in FIG. 1.Water is not useful in the hybrid system since it is not a propellant inthe liquid form as is hydrazine and hydrogen peroxide. With water,however, the option of either igniting the gnerated gases (by means ofcatalysts, glow plugs, or spark plugs) or using them in the cold gastechnique is available. The same engine (2 8 and 29 in FIG. 1) can beused for either method of gas propulsion; combustion chamber and sparkplug merely being surplusage in the cold gas technique.

When water is employed in the spherical chamber 20, bubbles of oxygengas (0 are generated at the surface of the anode while bubbles ofhydrogen gas (H are generated on the cathodic wall of the chamber 20.These bubbles slowly build up a supply of pressurized intermixedhydrogen and oxygen gas within the chamber.

Some advantages of using water as a propellant are that it is a stableinert fiuid which does not form gum or sludges during long storageperiods and does not require superinsulations for storage or boil-off.In addition, water has a high density compared to many propellants whilethe oxygen and hydrogen gases which are evolved are high performancepropellants when burner or ignited in the engine.

In order to aid the electrolysis action on the water, an electrolytesuch as potassium hydroxide is added to the water to set up anelectrolyte concentration of 0.4 normal, that is, 0.4 gram mole perliter. As the Water is used up for gas generation, the concentration ofthe potassium hydroxide (KOH) increases. As the concentration soincreases, less power is needed to generate a predetermined quantity ofgas. As a result, this system has the advantage of requiring less powerto operate as the mission life increases, thereby increasing thereliability of the system to compensate for againg or deterioration ofthe power source or solar cell array 51.

During the storage times, the two gases have an exact mixture ratio of8: 1, as fixed by the composition of water. As a result, mixture ratioshifts are not possible with this system, thereby insuring a constanthigh specific impulse of around 360 seconds; that is, a constant thrustper pound of propellant burned per second. In addition, the hydrogen andoxygen gas mixture is easily ignited, resulting in a fast transientresponse, is smooth and rapid burning, requires low combustionpressures, and does not form solids or residues. As a result, the enginelife is quite long and the operation quite reliable over extended timeperiods. As a result of these characteristics, pulses having the highlypredictable waveform such as the pulse graphically illustrated in FIG.4, are generated.

FIG. 6 illustrates an engine of the type in which the gas mixturegenerated from the electrolysis of water is fed into a combustionchamber and ignited. With the solenoid valve 26 open, the gaseouspropellant flows through a porous flashback prevention plug 57 into acombustion 7 chamber 58 of the engine 28. The engine 28 is of a thinwall diverging nozzle design and can be made of oxygenfree copper. Aheat sink 59 comprising a large mass of metal is formed at the inlet endof the engine for receiving and storing heat from the nozzle, therebypreventing excessive temperatures in the porous plug 57, gas manifold46, or the solenoid valve 26. The spark plug 30 is threadably connectedthrough the thin wall portion of the engine 28 to communicate with thecombustion chamber 58. The electrodes of this spark plug 30 areapproximately flush with the combustion chamber wall to aid rapidignition of the gas and insure long electrode life in this particularembodiment. Spark plug 30 can be a Champion Model V-2 or its equivalent.

At the same time that the propellant control valve 26 is opened a highvoltage AC signal is supplied to the spark lug 30. A command signal fromthe conventional telemetry circuit (not shown) closes a control switch61 of FIG. 5, thereby supplying electrical power to the propellantcontrol solenoid valve 26 and a chopper circuit 62. Control switch 61can be of any conventional electromechanical or electronic type andmerely conducts the DC power supply current to the chopper 62 andpropellant control valve 26. The chopper 62 in turn can 'be anyconventional free-running vibrator such as the type described in Fig.10.7 on p. 173 of the previously referenced Transistor Circuit Design.Frequency ranges for the AC output of this chopper would be from 3 to 10kilocycles. For circuit stability of the chopper 62, a reference circuitincluding a voltage reference source 63 and a trigger circuit 64 areconnected between the DC input power and the chopper 62 so as to providea stable voltage reference and close frequency control of the triggercircuit 64. As a resut, the frequency control of the chopper 62 isstabilized for varying load conditions. Voltage reference circuit 63 andtrigger circuit 64 are of the conventional type such as the previouslyreferenced voltage reference circuit 63 and trigger circuit 64,respectively. The AC output from the chopper 62 is fed to the primary ofan ignition coil 66 to greatly increase the voltage. A representativevoltage output from the ignition coil would be 13,000 volts.

In operation, as the gaseous propellant enters the engine combustionchamber the gases do not ignite until the chamber pressure reaches acertain low level. At this time, the spark plug 30 arcs to ignite thegases, thereby propagating a self-sustaining flame. This flame standsoif downstream from the porous flashback prevention plug 57. Since thespark plugs do not are in a vacuum, it is possible to use a single highvoltage ignition system for a multiple engine arrangement. Thus, the gasflow is actually used to initiate the arcing of the plug. As a result,the ignition system has the advantages of simplicity and reliability.

Porous plug 57 prevents flashback of the flame into the gas generationsystem by cooling or quenching the flame when it gets too close to thedownstream surface thereof. To perform this function, the porous plug 57is made of heat-conducting material, is in good mechanical contact withthe heat sink 59 of the engine and has sufficient structural strength towithstand the shock waves created during gas ignition. One type ofporous plug which has been found to be especially suitable is sinterednickel about Vs inch thick having a pore size of ten microns to 100microns. The effect of pore size is to change the pressure drop acrossthe plug and thus, the particular pore size is a matter of choice.

When a signal is given to stop the engine, the solenoid valve 26 isclosed and the chopper 62 cut off. The residual propellant entrappedbetween the solenoid valve and the combustion chamber is rapidly burnedto quickly cut off the engine thrust, thereby enabling accurate controlof the pulse period (FIG. 3). An advantage of using a gaseous propellantis that there is no dribble of propellant once the solenoid valve isclosed, thereby insuring quick pulse cut off. In addition, because ofthe fixed mixture ratio of the gases generated from water the pulsemagnitude is relatively constant and predictable.

In another embodiment of the invention illustrated in FIGS. 7 and 8,there is no need to spin the storage and electrolysis tanks about acentral axis, for example, as in the use of the present invention in aspinning satellite. Where the satellite is spinning, advantage is takenthereof by using centrifugal force to maintain the electrolyzablematerial in contact with the electrodes and also to ensure separation ofthe generated gas from the material. Instead, a spherical tank 71 isprovided with a cylindrical electrolysis cell 72 connected by a boltedflange 73 to project inwardly from one wall of the chamber 74. Indescribing this embodiment, it should be understood that there is acertain amount of duplication with the elements of the previouslydescribed embodiment. Accordingly, those elements which are similar areidentified by the same reference characters throughout the description.

The electrolysis cell 72 is illustrated in more detail in FIG. 8 and hasa water absorbent wick 76 inserted between a cathodic grid 77 and ananodic grid 78 to continuously feed water to the surface of theseelectrodes or grids by capillary action. More specifically, cell 72includes a hollow cylindrical outer housing 81 which is secured toproject from one face of the flange 73. Both the flange 73 and thecylindrical housing 81 are made of electrically-conducting metal and areat the same potential as the tank 71. The cylindrical cathodic grid orcathode 77 is made of nickel wire mesh and is inserted or positionedalong the inside wall of the cylindrical housing 81 to provideelectrical contact therewith. The hollow cylindrical wick 76 is made ofsome water-absorbent material of the type which is subject to capillaryaction, such as asbestos felt or plastic foam. The convoluted anodicgrid or anode 78 is made of wire mesh and is mounted adjacent the innerwall of the wick 76. Electrolyzing current is supplied to the anode 78from the DC-DC power converter 52 by means of a power lead 83 which isinsulated from the housing. An apertured cap 84 made of electricallyinsulating material is threadably connected to the open end of thecylindrical housing 81 to hold the electrodes and wick in place and toallow escape of evolved gas into the chamber 74.

In operation, water enters the electrolysis cell through the threadednipple 86 and passageway 87 from, for example, a collapsible bladder orcontainer and passes into a water storage chamber 88. The wick 76 isthen saturated carrying water into contact with the cathode 77 and anode78 to form hydrogen gas (H at the surface of the cathodic grid 77 andoxygen gas (0 at the surface of the anodic grid 78. The hydrogen gasescapes along the interspace formed between the cathode grid wires andthe housing wall and out through the gas clearance space formed betweenthe wick 76 and the inner face of the cap 84. Oxygen gas (0 in turnescapes through a hollow interior space formed within the grid wires ofanode 78. These gases then escape into the chamber 74 through theapertures in the cap. As the wick tends to dry out in the vicinity ofthe electrodes additional Water is brought into contact with theelectrode surfaces by the capillary action of the wick.

The operation of the propulsion system illustrated in FIGS. 7 and 8 issomewhat similar to the operation of the previously describedembodiment. As the gas pressure builds up in the spherical chamber 71,the pressure switch 23 is closed to cut off the power supply to theanode, thereby stopping the electrolysis action. When it is desired toobtain thrusting, the solenoid valve 26 is opened to feed gas through aporous plug into the combustion chamber of engine 28. At the same time,the chopper 62 is actuated to supply a high potential AC voltage to thespark plug 30, thereby igniting the gases to obtain a thrust force fromthe escaping gases.

As stated above the gas generated by electrolysis according to thepresent invention can be used in the cold gas technique or by burning inthe combustion chamber of an appropriate engine. The cold gas techniqueis known and is used, for example, with nitrogen in the Surveyorattitude control system. An engine for producing thrust in the cold gastechnique does not need a combustion chamber or spark plugv A suitableengine 100 is shown in FIG. 3 and consists simply of an exhaust nozzle102 connected very close to the solenoid actuated valve 26.

The cold gas technique has the advantage over the burning of gases inthat it is potentially more reliable. Although the thrust produced by agiven. quantity of propellant using the cold gas technique is less thanthat which would be produced by burning the same gases (assuming thesegases are burnable), for very long lifetime missions the addedreliability of the cold gas technique could justify the additionalweight required by its use. The engine 100 shown schematically in FIG. 3can be any of the well-known reaction engines presently used in the coldgas technique.

When designing a propulsion system which is to use only the cold gastechnique, reaction engines such as shown in FIG. 3 would be used.However, if a propulsion system employed a reaction engine as shown inFIG. 1 and if such a system had a fault in the apparatus for burning thegases, such a system could then still be used by employing the cold gastechnique. The gases would still flow through porous plug 57 and producea thrust force. The efliciency would be somewhat less than a systememploying an engine such as shown in FIG. 3.

The thrust producing device of the present invention is not limited inuse for propelling a spacecraft. It can be used to propel any type ofvehicle and can be used to produce a thrust on a stationary body forvarious purposes. It is especially useful where the vehicle or body isinaccessible and where it is on an extended mission whereby it isnecessary to provide a long lasting fuel supply system. Various types ofremotely controlled undersea instrument carrying vehicles or bodies havefuel requirements somewhat similar to those of spacecraft. The termvehicle as used throughout the present specification and claims isintended to include all such spacecraft, spaceprobes, undersea vehicles,bodies or probes regardless of their movement relative to theirimmediate surroundings. The present invention is useful on such vehiclesto produce a thrust for such purposes, for example, as to reorient ormove the vehicle, open a shutter, move a lever, or turn a rotor togenerate electricity. In the case where the gas generated byelectrolysis is not burned (e.g. in the cases where both hydrogen andoxygen are generated), it is not necessary that all of the gas go to thethrust producing device. For example, the oxygen could be fed to a lifesupport system and only the hydrogen used for thrust. Variouseelctrolyzable materials, preferred examples of which have been givenabove (i.e. water, hydrazine, and hydrogen peroxide) can be used in thisinvention in the liquid state or even in the solid state. This inventionis also useful as a pressurant generator for the expulsion of a liquidpropellant. In such a situation, the generated gas communicates with thechamber of a liquid propellant tank to exert a propulsion force on thepropellant. An advantage of this type of pressurant generation is thatslow leaks are compensated for by the system being able to replenish thelost gases.

While the salient features of the invention have been illustrated anddescribed with respect to particular embodiments it should be readilyapparent that numerous modifications may be made within the spirit andscope of the invention and it is therefore not desired to limit theinvention to the exact details shown.

What is claimed is:

1. A propulsion system which is capable of operating under zero gravitycondition comprising: an electrolysis tank forming an enclosed chamberfor storing a quantity of water; an electrode means mounted within thecham- Cir ber spaced from and electrically insulated from the chamberwall; power means connected to supply electrical current to saidelectrode at a potential difference relative to the potential of saidtank for electrolyzing the water Within the chamber whereby oxygen gasand hydrogen gas are evolved; mechanical means connected to said tankfor physically separating the water from the gas and maintaining thewater in contact with the surfaces of said electrode means; an enginehaving a combustion chamber formed therein; tube means connected tocommunicate the enclosed chamber with the combustion chamber of saidengine to provide a path for flowing gases thereinto; a porous plug ofheat-conducting material secured to said engine adjacent the combustionchamber and across the path of communication of said tube for passinggas to the combustion chamber and preventing flame flashback from thecombustion chamber to the electrolysis chamber; and an electricalignition system having electrodes connected in communication in saidcombustion chamber for arcing and igniting the gas contained therein.

2. A propulsion system of the type which can operate under weightlessconditions for extended periods of time comprising: an electrolysis tankforming an enclosed chamber for storing a quantity of water; anelectrode mounted within the chamber spaced from and electricallyinsulated from the chamber wall; power means connected to supplyelectrical current to said electrode at a voltage relative to thevoltage of said tank for electrolyzing the water within the chamberwhereby oxygen gas and hydrogen gas are evolved; mechanical meansconnected to said tank for physically separating the water from the gasand maintaining the water in contact with the relatively cathodicsurfaces created by the potential difference between said electrode andsaid tank; an engine having a combustion chamber formed therein; tubemeans connected to communicate the enclosed chamber with the combustionchamber of said engine to provide a path for flowing gases thereinto; aporous plug of heat-conducting material secured to said engine adjacentthe combustion chamber and across the path of communication of said tubefor passing gas to the combustion chamber and preventing flame flashbackfrom the combustion chamber to the electrolysis chamber; a valve meansconnected in said tube to selectively block and open the path forflowing gases; and an electrical ignition system having electrodesconnected in said combustion chamber for arcing and igniting the gascontained therein.

3. A rocket propulsion system of the type that is operable in a zerogravity field comprising: an electrolysis tank forming an enclosedchamber for storing a quantity of water; an electrode mounted within thechamber spaced from and electrically insulated from the chamber wall;power means connected to supply electrical current to said electrode forelectrolyzing the water within the chamber whereby oxygen gas andhydrogen gas are evolved; means connected to centrifugally spin theelectrolysis tank to separate the water from the gases such that thewater surrounds said electrode; a reaction engine having a combustionchamber formed therein; tube means connected to communicate the enclosedchamber with the combustion chamber of said engine to provide a path forflowing gases thereinto; a porous plug of heat-conducting materialsecured to said engine adjacent the combustion chamber and across thepath of communication of said tube for passing gas to the combustionchamber and preventing flame flashback from the combustion chamber tothe electrolysis chamber; and an electrical ignition syspower meansconnected to supply electrical current to said electrode forelectrolyzing the water within the chamber whereby oxygen gas andhydrogen gas are evolved; means connected to centrifugally spin theelectrolysis tank to separate the water from the gases such that thewater surrounds said electrode; a reaction engine having a combustionchamber formed therein; tube means connected .between said tank and saidengine for communicating the enclosed chamber with the combustionchamber of said engine and providing a path for flowing gasestherebetween; a porous plug of heat-conducting material secured to saidengine adjacent the combustion chamber and across the path ofcommunication of said tube means for passing gas to the combustionchamber in one direction and preventing flame flashback from thecombustion chamber to the electrolysis chamber in the other direction; avalve means connected in said tube to selectively block and open thepath of communication for flowing gases; and an electrical ignitionsystem having electrodes connected in said combustion chamber for arcingand igniting the gas contained therein.

5. A propulsion system comprising: an electrolysis tank forming anenclosed chamber; an electrode means mounted within the chamber spacedfrom and electrically insulated from the chamber wall; electrical powermeans including a solar cell array connected in circuit with saidelectrode means to supply electrical power; a control switch meansconnected between said power source and said electrode for supplyingelectrolyzing current thereto for generating hydrogen gas and oxygen gasfrom the water; a pressure-sensitive switch connected in fluid communication with the chamber of said tank whereby said switch is actuatedat a predetermined threshold chamber pressure, said pressure-sensitiveswitch being connected to open said control switch when the fluidpressure of the enclosed chamber exceeds the threshold pressure and toclose said control switch when the fluid pressure of the enclosedchamber is less than the threshold pressure; an engine having acombustion chamber formed therein, said engine being connected to saidtank in gas communication with the chamber thereof; a control valveconnected between said tank and said engine to selectively open andclose the path of gas communication therebetween; arc-generating meansincluding electrodes connected to said engine in communication with thecombustion chamber thereof; propulsion switch means connected to saidcontrol valve and said arc-generating means for simultaneously openingsaid control valve and energizing said arc-generating means whereby gasflowing into the combustion chamber is ignited; and a porous plug ofheat-conducting material secured to said engine adjacent the combustionchamber for passing gas to the combustion chamber and preventingflashback of the gas flame into the chamber of said tank.

6. A rocket propulsion system comprising:

an electrolysis tank forming an enclosed chamber for storing a quantityof water and gas;

an electrolysis electrode means mounted to said tank in gascommunication with the chamber;

a solar cell panel for generating electrical power;

an electrolyzing current control switch connected between said solarcell and said electrode for selectively supplying current to theelectrode for generating hydrogen gas and oxygen gas from the water;

a pressure-sensitive switch connected to said tank in gas communicationwith the chamber thereof to be actuated at a predetermined thresholdpressure, said pressure-sensitive switch being connected to saidelectrolyzing current control switch to close said control switch whenthe gas pressure exceeds the threshold level and to open said controlswitch when the gas pressure falls below the threshold pressure;

a reaction engine having a combustion chamber, said engine beingconnected to said tank in gas communication with the enclosed chamberthereof, a gas flow control valve connected between said tank and said12 reaction engine for selectively opening and closing the path of gascommunication therebetween;

a porous plug of heat-conducting material secured to said engineadjacent and downstream of the combustion chamber and across the path ofgas communication between the chamber and said engine;

a spark-generating means including electrodes connected to said enginein communication with the combustion chamber thereof;

and a propulsion control switch connected to said control valve and saidspark-generating means for simultaneous energizing or de-energizing saidgas flow control valve and spark-generating means for igniting orturning off the propelling force respectively.

7. A thrust producing apparatus comprising:

a tank connected and adapted to contain a liquid propellant from whichgas can be generated by passing an electrolytic current therethrough;

means for electrolyzing said propellant to generate gas;

means for receiving said generated gas and for storing it underpressure;

means for stopping said electrolysis when the pressure of said storedgas reaches a predetermined pressure;

a first thrust producing engine adapted for use with said liquidpropellant to produce thrust;

feed lines means connected between said tank and said first engine forfeeding said liquid propellant to said engine;

valve means in said feed line means for controllably feeding said liquidpropellant to said first engine;

a second thrust producing engine adapted for use with said generated gasto produce thrust;

gas feed line means connected between said receiving and storing meansand said second engine for providing gas communication therebetween; and

valve means in said gas feed line for controllably feeding saidgenerated gas to said second engine.

8. The apparatus according to claim 7 including:

means for providing gaseous communication between said generated gas andsaid liquid propellant whereby said liquid propellant is fed to saidfirst engine under pressure of said generated gas.

9. A thrust producing apparatus comprising:

a tank adapted to contain a quantity of hydrazine;

means for electrolyzing said hydrazine to generate gas;

means for receiving and storing said generated gas under pressure;

means for stopping the said electrolysis of said hydrazlne when thepressure of said generated gas reaches a predetermined pressure;

a liquid hydrazine engine;

feed line means connected between said tank and said engine for feedingsaid liquid hydrazine to said engme;

valve means in said feed line means for controllably feeding said liquidhydrazine to said engine;

a gas engine adapted for use with said generated gas to produce thrust;

gas feed line means connected between said receiving and storing meansand said gas engine for providing gas communication therebetween; and

valve means in said gas feed line for controllably feed ing saidgenerated gas to said gas engine.

10. A thrust producing apparatus comprising:

a tank adapted to contain a quantity of liquid material from which gascan be generated by passing an electrolytic current therethrough;

means for electrolyzing said material to generate gas;

means for receiving and storing said generated gas under pressure;

means for stopping said electrolysis when the pressure of said generatedgas reaches a predetermined pressure;

an engine adapted for use with said generated gas to produce thrust;

a feed line connected between said receiving and storing means and saidengine to provide gas communication therebetween;

valve means in said feed line for controllably feeding said generatedgas to said engine; and

means for centrifugally maintaining said material in contact with saidelectrolyzing means whereby the centrifugal force also effectscentrifugal separation of the generated gas from said material.

References Cited UNITED STATES PATENTS 1,281,962 10/1918 Holland.1,581,944 4/1926 Hausmeister 204-429 Holland.

Knowlton 204129 XR Cowan 219-274 Turner 219-474 Goddard 6039.11

Toulmin 136-206 Kitchen et a1. 60-39.11 XR Cole 204--129 XR McLean.

Kenney 60-204 Rhodes et al 204129 XR CARLTON R. CROYLE, Primary ExaminerU.S. Cl. X.R.

